The development of sheets of microporous foams is the subject of substantial commercial interest. Such foams have found utility in various applications including thermal, acoustic, electrical and mechanical insulators, absorbent materials, filters, membranes, floor mats, toys, carriers for ink, dyes, lubricants and lotions. In the field of absorbent articles, such as disposable diapers, adult incontinence pads and briefs, and catamenial products such as sanitary napkins, the ability to provide higher performance is primarily contingent on the ability of the core to acquire, distribute, and store large quantities of discharged body fluids. Open-celled polymeric foams are one example of absorbent materials capable of acquiring, distributing, and storing large quantities of discharged body fluids. Absorbent articles containing such foams can possess desirable wet integrity, can provide suitable fit throughout the entire period the article is worn, and can minimize changes in shape during use (e.g., uncontrolled swelling, bunching). In addition, absorbent articles containing such foam structures can be easier to manufacture on a commercial scale. For example, absorbent diaper cores can simply be stamped out from continuous foam sheets and can be designed to have considerably greater integrity and uniformity than absorbent fibrous webs. Such foams can also be prepared in any desired shape, or even formed into single-piece diapers.
Particularly suitable absorbent foams for high performance absorbent articles such as diapers have been made from High Internal Phase Emulsions (hereafter referred to as "HIPE"). See, for example, U.S. Pat. No. 5,260,345 (DesMarais et al), issued Nov. 9, 1993 and U.S. Pat. No. 5,268,224 (DesMarais et al), issued Dec. 7, 1993, hereby incorporated herein by reference. These absorbent HIPE foams provide desirable fluid handling properties, including: (a) relatively good wicking and fluid distribution characteristics to transport the imbibed urine or other body fluid away from the initial impingement zone and into other regions of the foam structure to allow for subsequent gushes of fluid to be accommodated; and (b) a relatively high storage capacity with a relatively high fluid capacity under load, i.e. under compressive forces.
When formed into sheets or webs, these HIPE absorbent foams are also sufficiently flexible and soft so as to provide a high degree of comfort to the wearer of the absorbent article; some can be made relatively thin until subsequently wetted by the absorbed body fluid. See also U.S. Pat. No. 5,147,345 (Young et al), issued Sep. 15, 1992 and U.S. Pat. No. 5,318,554 (Young et al), issued Jun. 7, 1994, which discloses absorbent cores having a fluid acquisition/distribution component that can be a hydrophilic, flexible, open-celled foam such as a melamine-formaldehyde foam (e.g., BASOTECT made by BASF), and a fluid storage/redistribution component that is a HIPE-based absorbent foam.
For use in absorbent articles as part of an absorbent core, the block of water-filled foam is preferably formed into relatively thin sheets and dewatered. The polymerized HIPE foam is typically cut or sliced to provide a sheet thickness in the range from about 0.08 to about 2.5 cm. Often the polymerized HIPE foam is cut or sliced into sheet form prior to dewatering since sheets of polymerized HWE foam are generally easier to process during subsequent treating/washing and dewatering steps. It is also preferable that continuous webs of dewatered foam material be formed and be converted to roll stock, suitable for subsequent processing into absorbent cores in a continuous process.
Currently, HIPE foam production is batch processed by curing (polymerizing) a high internal phase emulsion in large tubs or vats. Once cured, the resulting block of material is a water-filled, open-celled foam. By water-filled is meant that the porous structure is substantially filled with the residual water phase material used to prepare the HIPE. This residual water phase material (generally an aqueous solution of electrolyte, residual emulsifier, and polymerization initiator) is typically about 90-99% by weight of the cured HIPE foam. The cured foam block is often substantially cylindrical in shape, the shape being determined by the shape of the tub or vat, which is essentially a mold. Until now, in a typical batch process, the cured, water-filled foam block was generally cylindrical in shape, approximately 40-60 inches in diameter, approximately 24 inches high, and weighed from 450-3000 pounds. The size and weight of the block, was generally limited by the post-formation processing techniques and the physical characteristics of the block material.
Due to the size, weight, and structural integrity of the water-filled, porous block after curing, forming continuous webs of uniform thickness is not economically practical or technically feasible by known methods such as veneering, or cutting by use of conventional saws. For example, the weight and structural integrity of the foam block requires it to be fully supported during any subsequent processing, including cutting or slicing continuous webs or sheets. If not fully supported, the block can collapse or deform causing the cutting, slicing or other processing to be uneven or ineffective.
Although commonly assigned U.S. patent application Ser. No. 08/939,172, entitled "Method And Apparatus For Producing A Continuous Web From A Block Of Material" filed Sep. 29, 1997 in the names of David Albert Sabatelli, et al. describes an apparatus and method suitable for slicing a cured foam block, such as a HIPE, the method is somewhat complex and does not specifically address the difficulties with handling very large blocks of foam or blocks of very soft materials, wherein simply supporting the block upon its base is insufficient to maintain the shape of the block.
Additionally, dewatering of the continuous web as well as other processing generally requires that the web be moving at a constant rate to provide reliable and repeatable results. Therefore, cutting or slicing the continuous web of water-filled HIPE foam from the perimeter of a cylindrical block is preferably accomplished as the block is rotating at a constant tangential velocity rather than a constant angular velocity.
Accordingly, it would be desirable to be able to form continuous webs of material from a monolithic block of material. Additionally, it would be desirable to be able to form continuous webs of material from a monolithic block supported in such a manner as to minimize deformation of the block prior to cutting or processing. Also, it would be desirable to be able to form a continuous web of water-fired HIPE foam material from a cured block of foam material. Further, it would be advantageous to be able to form continuous webs of foam material in an automated process such that webs of uniform thickness are produced at a uniform linear velocity. Even further, it would be desirable to increase efficiencies of scale by providing a method for cut very large blocks of material or blocks of soft material which could not have been effectively handled with prior art cutting and handling techniques.